The invention relates to a crucible for use in heating and/or retaining melts at elevated temperatures.
Generally, prior art crucibles of this type are composed of one of the platinum metals such as iridium having a melting point of 2,454.degree. C. In the case of crystal growing, a melt is prepared and a seed crystal is introduced therein while the temperature and movement of the seed crystal from the melt is controlled to produce a cylindrical crystal.
The prior art iridium crucibles have been found to be disadvantageous because of the short term of use due to corrosion. Iridium is relatively resistant to oxidizing substances but the corrosion results from the extended period of time which can be from a few hours to a few days for the crystal growing process. The corrosion of the inside surface of the crucible by certain melts causes the inside of the crucible to become rough and increases the exposed surface area so that the corrosion process is increased. The corrosion process is known to be a function of temperature and is highest in the regions of the higher temperatures.
In the case of a crucible heated directly by the field of an induction coil, an uneven temperature distribution along the crucible axis arises due to asymmetry and inhomogeneity.
The relatively short period of use for a crucible sometimes requires a change in the crucible being used for a process requiring a relatively long period of time. The high cost of iridium compels the salvaging of the corroded crucible for use to form a new crucible. Even when the used crucibles are used to produce a new crucible, the production costs are very high because the iridium can only be processed at a temperature of about 1,200.degree. C.
The instant invention endeavors to eliminate many of the known disadvantages of the aforementioned crucibles including the reduction of corrosion, the reduction of production costs for the material, and the reduction of the cost for molding the crucibles.